Purpose :
Dry environments, such as those in offices or air craft cabins, can potentially generate ocular discomfort and alter the tear film. We compare various optical and non-optical parameters in young and older subjects after exposure to dry conditions using a controlled environmental chamber (CEC).

Methods :
Twenty-four healthy subjects, covering an age range between 18 to 83 years old, were recruited. Subjects watched a movie (for 1.5 hours) in a CEC with a constant temperature (23°) and low humidity (5%). Various parameters were measured before and after the exposure: i) Objective Scatter Index (OSI) of the eye (OQAS, Visiometrics, Spain), ii) Blinking period over a 5 minutes video using customized image processing routines to detect blinks iii) Tear Film Homogeneity (TFH) using a specially built instrument which recorded the corneal reflection of a 300 LEDs-ring at 100 fps for 45 seconds. A metric, based on the cross-correlation function, was used to assess the tear film during inter-blink periods. Subjects also completed a questionnaire (OSDI) to score symptoms related to dryness.

Results :
Light scatter did not change in younger subjects (<40 y.) but increased significantly in older subjects (>60 y.) (p=0.013) after exposure to the dry conditions, and that change was linearly correlated with age when all the data were pooled together (R=0.42; p=0.043). Subjective complaints and light scatter did not correlate significantly, although subjects who showed a large increase in light scatter (four were above a change of 0.25 units of OSI) also reported increased dryness. Blinking period decreased significantly after exposure (p=0.002) in both younger and older subjects with older subjects showing a larger mean difference (-1.0±0.8 sec in younger subjects, -2.6±2.8 sec in older subjects). TFH assessed from corneal reflection did not show statistically significant changes in younger and older subjects, but did deteriorate more in those subjects who had symptoms compared to those without symptoms (unpaired t-test p=0.02).